Electric circuits for an electric motor car include a main circuit that supplies power to an electric motor, and an auxiliary circuit that supplies power to auxiliary devices, such as an air conditioner for the interior of the vehicle, and lighting devices.
In the case of AC electric motor cars that run upon reception of AC power supply from an overhead line, at the time of power running, the AC power supplied from the overhead line is sequentially converted by a main transformer and a main conversion device both constructing the main circuit, and is output to the electric motor. Hence, the power is converted to motion energy, and thus electric motor cars can run.
Typically, this main conversion device includes first and second power converters, and an intermediate link that electrically connects those converters. At the time of power running, the first power converter converts AC power output by the main transformer to DC power, and outputs this DC power to the intermediate link. The second power converter converts, at the time of power running, the DC power supplied from the intermediate link to AC power, and outputs this AC power to the electric motor.
An auxiliary power-supply device (APS) that is the power source for the auxiliary circuit is connected with the main circuit to receive power.
Typically, the auxiliary power-supply device provided separately from the main conversion device is directly connected with the main transformer. In this case, the power supplied from the overhead line is supplied to both main conversion device and auxiliary power-supply device through the main transformer.
Conversely, an auxiliary power-supply device integrally provided with the main conversion device is typically connected with the intermediate link in the main conversion device (see, for example, Patent Literature 1). In this case, the power supplied from the overhead line is supplied to both second power converter and auxiliary power-supply device through the main transformer and the first power converter.
Meanwhile, in recent years, there are electric motor cars which utilize, at the time of braking, the electric motor as a power generator to convert the motion energy of the vehicle to power through the main circuit thereby causing regenerative power to flow to the overhead line. The regenerative power to the overhead line results in the reduction of power consumption, but the regenerative power generated by the electric motor often contains harmonic components. Because of the reasons such that the transformer of a transforming station is not compatible with such harmonic components, regenerative power to the overhead line is sometimes restricted to be equal to or smaller than a predetermined value (including zero).
In the case of the auxiliary power-supply device that is separately provided from the main conversion device, the main conversion device and the auxiliary power-supply device can operate independently. Hence, when regenerative power to the overhead line is restricted, the operation of the first power converter is terminated, and thus the regenerative power flowing to the overhead line is shut down. Hence, the adverse effects of harmonic components to the transforming station can be avoided. Even if the first power converter is deactivated, the auxiliary power-supply device can receive power supply from the overhead line through the main transformer, and thus the auxiliary power-supply device can continuously supply power to the auxiliary devices.